A vehicle has been developed and has become commercially practical that is mounted with a powertrain called hybrid system combining an internal combustion engine (any known engine such as gasoline engine or diesel engine may be used for example) with an electrical motor. Such a vehicle is mounted with electrical devices including a secondary battery for driving a travel-purpose electrical motor which serves to cause the vehicle to travel, as well as an electric power conversion device (PCU (Power Control Unit)) such as inverter and DC/DC converter. The secondary battery is discharged and charged through a chemical reaction. The chemical reaction is accompanied by heat generation, and therefore, the secondary battery has to be cooled. In the inverter and the DC/DC converter as well, heat is generated from power elements. Therefore, the inverter and the DC/DC converter also have to be cooled. In the electrical devices, generally Joule heat is generated when electric current flows through an electric power line. It is therefore necessary to cool the electrical devices.
The electrical devices (such as secondary battery (battery) and PCU) are in some cases disposed for example under the backseat of the vehicle or between the backseat and the luggage area of the vehicle. The electrical devices are placed in a casing connected to a duct serving as an air passage. On the upstream (or may be downstream) side of the intake airflow with respect to the electrical devices in the casing, a cooling fan generating a cooling air for cooling the electrical devices is provided. Since the upstream end of the casing communicates with the vehicle interior (specifically communicates with the vehicle interior through an intake opening of a duct provided on the floor panel in front of the backseat or an intake opening in a rear package tray). Therefore, the electrical devices are cooled by the air within the vehicle interior.
For the secondary battery, a nickel-metal hydride battery or lithium-ion battery for example is used. Regarding such a secondary battery (the following example of the battery pack refers to the one using the nickel-metal hydride battery), the output voltage per cell is approximately 1.2 V. Six cells are series-connected to configure a battery module with an output voltage of 7.2 V. The secondary battery is mounted on the vehicle in the form of a battery pack with an output voltage of 216 V to 288 V configured by series-connecting 30 to 40 battery modules. The battery pack is divided into three to five battery units to be mounted on the floor panel of the vehicle or under the floor of the luggage area.
Since the hybrid vehicle has to be mounted with such electrical devices as described above in addition to the engine, it is difficult to provide a cooling passage such that the cells of the secondary battery with a large volume are equally cooled.
The secondary battery is controlled using SOC (State Of Charge) representing the remaining capacity of the battery, such that SOC is kept in a predetermined range. In the vehicle caused to travel by driving the electrical motor using electric power from the secondary battery, the quantity of electric power that can be input/output to/from the secondary battery has a significant influence on the traveling performance of the vehicle. Due to various factors, the quantity of electric power that can be input/output to/from the secondary battery varies. The battery temperature is one of the influential factors. It is therefore important to manage the temperature of the secondary battery. Further, if any abnormality occurs, the temperature of such a secondary battery could become abnormally high. Thus, the hybrid vehicle travels while whether or not an abnormality occurs is monitored.
Japanese Patent Laying-Open No. 2001-25103 discloses a drive apparatus for a hybrid vehicle that can ensure the main-battery (travel-purpose battery serving to cause the vehicle to travel) protection capability while avoiding deterioration in vehicle traveling capability. The drive apparatus for the hybrid vehicle disclosed in this publication includes: an engine; a main battery; an energy transmission apparatus controlling supply and receipt of energy between the engine, the main battery and a vehicle driveshaft, converting engine power into electric power to charge the main battery, and converting the electric power of the main battery into motive power to start the engine; a control apparatus controlling the energy transmission apparatus; a battery abnormality detection apparatus detecting an abnormality of the main battery; and a switch apparatus opening and closing an electrical transmission passage between the main battery and the energy transmission apparatus. The control apparatus has a feature as follows. When an abnormality of the main battery is detected while the engine is stopped in spite of vehicle travel mode, the control apparatus gives an instruction to start the engine, inhibits charge/discharge of the main battery by breaking the switch apparatus after the start of the engine is completed, inhibits the engine from being stopped in the vehicle travel mode, and operates the energy transmission apparatus in a control mode which does not involve supply and receipt of electric power from and to the main battery.
In the case where an abnormality occurs to the main battery while the vehicle is in the travel mode, the drive apparatus for the hybrid vehicle always disconnects the main battery after the engine operating state has been established, and therefore, the following problem does not occur. The problem is specifically that the vehicle cannot travel using the engine because the main battery is disconnected since an abnormality occurs to the main battery while the engine is stopped.
The drive apparatus for the hybrid vehicle disclosed in Japanese Patent Laying-Open No. 2001-25103 as described above causes the hybrid vehicle to travel using the engine, regardless of what abnormality occurs to the main battery. For example, there could be the case where, even if the charge and discharge of the main battery are inhibited, a chemical reaction of the secondary battery is proceeding. Japanese Patent Laying-Open No. 2001-25103 does not mention the problem that the hybrid vehicle continues traveling in such a case as described above.